Automotive glass sheets such as front windows or back lights are generally adhesively secured within window frames of automotive vehicles. Prior to installation, a number of preparation steps are required to insure that the adhesive properly secures the glass within the frame.
The first step is to chemically etch the marginal edge of the glass. This is accomplished by the application of a liquid primer which etches and cleans the glass surface. After applying this solution by brush, dobbing, spraying or other means, this primer is wiped away with a lint free substance to provide a clear, dry surface.
The second step is to apply a black primer to the etched edge of the glass prior to the application of a urethane sealant. The black primer protects the urethane sealant from sunlight which causes deterioration in the sealant. The black primer is applied by means of a brush, spray or drip and is allowed to dry. Then the urethane sealant is applied prior to installation of the glass in the vehicle.
A serious problem over the years has been to detect whether the primers, in particular the etching primer which is generally clear, ave been applied continuously along the marginal edges of the glass surface. If any primer, either the etching primer or the black primer, is not applied, the bonding of the urethane sealant may fail resulting in the glass coming free of the automotive vehicle.
Various approaches, i.e., camera systems, thermal sensors, and flow sensors have been experimented with and capacitative probes have been inserted into a brush applying the primers all in an effort to determine whether the sealant has been or is being applied to the glass. None of these approaches has proven satisfactory.
These means of detection of the primer coatings suffer from several disadvantages. First, typically a rather large quantity of primer must be present in order for these detection means to insure detection of their presence. A second problem is that these detection means generally indicate only whether a coating is present and do not readily quantify the amount present. Third, these means are not suitable to sense the presence of a coating on a glass surface as the sensing means moves relative to the glass surface.
Previous attempts at directing electromagnetic radiation perpendicularly downward towards a glass surface and measuring the difference between the reflectivity of a wet surface and a dry surface has proven unsuccessful in determining the presence or absence of a coating of primer.